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InfoQ Homepage News How Chirp Audio QR Codes Went to the Moon and Back

How Chirp Audio QR Codes Went to the Moon and Back

Chirp uses audio to send and receive data using only a device's speaker and microphone. Recently, Chirp had a chance to test their technology by sending signals to the Moon. InfoQ has spoken with Daniel Jones, chief technology officer at Chirp, to learn more about Chirp codes.

Chirp sends data using either audible or inaudible frequencies, enabling the exchange of data between devices without requiring the establishment of a network or pairing. The devices exchanging Chirp codes can share the same acoustic environment, e.g., a room, or use any medium able to carry audio, such as a telephone line. Given the intrinsic nature of audio, Chirp codes can be easily broadcast to multiple devices at hearing distance.

On the technical side, Chirp relies on frequency shift keying (FSK) for signal modulation. Chirp messages can include any specific sequences that are used to indicate the start and length of a message as well as support error detection and correction.

As mentioned, Chirp recently carried through an experiment and sent a Chirp audio code to The Moon:

The signal was heard from the computer speaker, followed by a moment's delay as it was beamed from the radio telescope and upwards through the earth's atmosphere. The moon-bounced response then crackled back through the Skype link, backed with cosmic static. Astonishingly, given the number of lossy links in the transmission pipeline, the transmission decoded first time.

The major advantages of data-over-audio technologies like Chirp are the ability to let devices communicate without the hassle of establishing a network setup or pairing. In addition, audio codes are useful in environments forbidding the use of radio-frequencies.

InfoQ has spoken with Daniel Jones, chief technology officer at Chirp, to learn more about Chirp codes.

InfoQ: Could you explain a few compelling use cases where Chirp audio codes could be used? What kind of existing technology do they improve upon or aim to replace?

Daniel Jones: Although there’s an array of connectivity technologies out there, data-over-sound fits a niche that no other technology quite fulfils: short-range, multi-way data transfer that happens at the tap of a button. Chirp’s USP is that it just works: no passwords or pairing, no need to enable Bluetooth, no problems with device support.

Another benefit of using sound as a medium is that it won’t carry through walls, unlike RF-based media like Bluetooth and Wi-Fi. That makes it suitable for tasks like room presence detection, in common scenarios like shared workspaces where you might have meeting room hubs in lots of adjoining rooms.

We’re working with providers to make meeting room hubs that send out Chirp ultrasonic beacons that can only be heard within that room, which contain all of the network information. You step into the room, your device detects exactly what room you’re in, receives the Wi-Fi credentials, connects to the network, and then connects to the meeting room screen. This is one of our favourite application areas as it solves so many pain points at once.

We’re also seeing a lot of uptake in IoT. One common use case is configuring smart devices with Wi-Fi credentials; instead of having to manually enter your password into each new smart device that you bring into your home, you can simply chirp them from your mobile device.

Chirp is also popular in toys and gaming, for tasks such as discovering nearby gamers and creating data links between the TV and accompanying second-screen devices.

InfoQ: What are the advantages of using inaudible audio codes for device-to-device communication?

Jones: The key advantages are:

  • It’s friction-less: Chirp doesn’t require any passwords or pairing. Any device that hears the tone receives the data.

  • It’s low-power and low-cost. Chirp is provided as a software-only solution, so if your device already has audio I/O, you won’t need to make any changes to your bill of material.

  • It’s universal: It runs on any mobile device made in the past 10 years, and can even be transmitted down simple channels like VoIP or streaming video.

  • It won’t pass through walls, which enables us to do room presence detection outlined above.

  • It’s secure and trustworthy: As it doesn’t pass any data to the cloud, it is safe from remote snoopers. You can layer industry-standard cryptography algorithms for private transactions.

InfoQ: What are the current limits of Chirp technology in terms of throughput, energy efficiency, reliability, overall quantity of data that can be exchanged?

Jones: Reliability has always been our key objective, as it’s so important for that friction-less experience. We’ve dedicated years of research time to solving these problems. And thanks to the optimisation work of our expert embedded engineers, Chirp requires very little power. It can run on sub-$1 microchips (Arm Cortex-M4 @ 64Mhz), and, paired with wake-on-sound microphones such as Vesper’s VM1010, uses less power than BLE.

Since the acoustic channel is very noisy, we must highlight that you’re not likely to see data rates anywhere near those of BLE. At typical peer-to-peer ranges, expect rates of 100-200bps. That’s enough to send an email address, token ID, or an encrypted set of credentials - but maybe not your home videos! At NFC range, we’re able to transmit at 1kbps.

InfoQ: What were/are the major technological stumble points you needed to solve to make Chirp codes work reliably?

Jones: For the first few years, we were firmly focused on the R&D necessary to make data-over-sound robust enough for noisy real-world environments. We began in a research lab in University College London, doing field tests in all sorts of noisy places - pubs, streets, rock concerts.

This was tested to its limits when we began trialling with EDF Energy on creating long-range ultrasonic links within their nuclear power stations, to solve the challenges they have with Wi-Fi restrictions in these sensitive environments. Remarkably, we were able to attain 100% data integrity over a long-duration, long-range test, even in the deafening 100dB surrounds of their turbine hall.

More recently, we’ve been porting the code to work on a wide range of IoT devices and focusing on power and optimisation. This has opened up the technology to a lot of new devices and form factors, most recently the new Arduino Nano 33 BLE Sense board.

InfoQ: Could you explain how the “Moon mission” came about? In what ways is your tech relevant to space missions? And what is the meaning of being able to send an audio code to The Moon and then decode it?

Jones: We were one of the technical sponsors of the first hackathon at Abbey Road Studios, where we met a talented artist called Martina Zelenika. She has an ongoing art project in collaboration with a radio observatory in the Netherlands, in which she bounces short fragments of audio off the surface of The Moon, encoded as RF signals, and decodes the reflected signal back here on earth.

We thought it would be wonderful to send the first Chirp signal to The Moon and back. And, in a testament to the decoder’s reliability, we were able to decode the noisy reflected signal first time.

It would be of limited use in real space missions as mature transmission schemes are already used which modulate data directly onto RF waves. In our version, we were sending data over sound over radio, which — although a fun experiment — is unlikely to be adopted by NASA any day soon!

Chirp is not the only data-over-sound solutions provider. Other players in the market include ITC Infotech, LISNR, Sonarax, and others.

Chirp provides a suite of cross-platform enterprise-ready SDKs that can be downloaded for free. Written in C, Chirp SDK supports Arduino, Android, iOS, Windows, all major browsers, and desktop OSes.

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